Rewritable recording medium capable of changing the length and start position of synchronization portion

ABSTRACT

A rewritable recording medium having a first adjustment region recorded with first signal information, a data portion recorded with data information after the first adjustment region, and second adjustment region recorded with a second signal information after the data portion. Each time the first signal information is rerecorded, a length of the first adjustment region changes and a start position of the first adjustment region changes.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 10/454,503, filedJun. 5, 2003, now U.S. Pat. No. 6,788,643, which is a continuation ofU.S. application Ser. No. 10/189,428, filed Jul. 8, 2002, now U.S. Pat.No. 6,580,673, which is a continuation of U.S. application Ser. No.09/949,640, filed Sep. 12, 2001, now U.S. Pat. No. 6,430,134, which is acontinuation of U.S. application Ser. No. 09/712,969, filed Nov. 16,2000, now U.S. Pat. No. 6,307,825, which is a continuation of U.S.application Ser. No. 09/535,016, filed Mar. 24, 2000, now U.S. Pat. No.6,181,661, which is a continuation of U.S. application Ser. No.09/350,282, filed Jul. 9, 1999, now U.S. Pat. No. 6,104,692, which is acontinuation of U.S. application Ser. No. 08/863,126, filed May 27,1997, now U.S. Pat. No. 5,953,299, the subject matter of which isincorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to a so-called mark-edge recording inwhich marks are recorded in certain areas of a recording medium so thattheir physical property is made different from the other areas tothereby have information associated with both ends of each of the marks.

The present invention is particularly suited to a rewritablehigh-density information recording method capable of recordinginformation to be repeatedly rewritable. The present invention is alsosuited to a so-called phase-changing type information recording methodin which the physical property of the information recorded areas is madedifferent from the other areas by the phase change of the recordedsubstance that is caused by changing the temperature of the informationrecording medium.

A conventional rewritable information recording method is disclosed in,for example, JP-A-63-229625. This method is an optical disk recordingmethod for recording information by modulating the intensity of light.

As shown in FIG. 6, information is recorded in a plurality of sectors21, each of which has identification information 24 provided at its headin order to indicate the physical position of information. Thisidentification information 24 is used as a reference to be followed by asynchronizing signal portion 22 and an information recorded portion 23which are recorded as a record unit on the recording medium. At thistime, the start position of the record unit is randomly changed in itsposition at each time of rewriting, thereby increasing the possiblenumber of times of repeated rewriting. In other words, the disk materialat the same place within a sector is prevented as much as possible frombeing deteriorated by repeated rewriting, thereby raising the possiblenumber of times of repeated writing.

FIG. 7 illustrates the relation between the number of times of rewritingand the jitter in the case where the same recording information isrepeatedly recorded. Here, the jitter is defined as the standarddeviation normalized by a reproduction detection window width, thestandard deviation being of the time shift between a reproduction clockand a reproduced data after the same random data is EFM-modulated,recorded repeatedly and then reproduced.

In FIG. 7, a curve 701 was obtained when the start position of therecorded portion is shifted by 2 bytes in the mark-edge recording, acurve 702 when shifted by 30 bytes in the mark-edge recording, a curve703 when shifted by 2 bytes in the mark-position recording, a curve 704when shifted by 100 bytes in the mark-edge recording, and a curve 705when shifted by 30 bytes in the mark-position recording. Here, themark-position recording is the recording system in which information isrecorded in association with the center position of the mark.

From FIG. 7, it will be seen that the increase of jitter after rewritingcan be suppressed more, or the possible number of times of rewriting isincreased as the amount of the shift of the start position of therecorded area is increased. Here, the minimum mark distance, in themark-position recording in which data is associated with the centerposition of the mark, was selected to be 0.9 μm, and the minimum markdistance, in the mark-edge recording in which data is associated withboth ends of the mark, was chosen to be 0.6 μm. In addition, thediameter of the recording and reproducing spot was 0.9 μm, and therecording medium used was a GeSbTe-based phase-change recording medium.

However, in the start-position shift system, and particularly in themark-edge recording, the shift of the start position of the randomlyrecorded data must be increased to about 100 bytes in order to achieve apractical possible number of times of rewriting, as will be understoodfrom FIG. 7, when the same information is repeatedly rewritten.Therefore, the utilization efficiency of sectors was greatly reduced. Inaddition, under this great positional shift, the beginning end or lastend of recorded information will be superimposed upon other recordedportions. Since the recording characteristics of the beginning end orlast end of recorded information are deteriorated probably due to thedissolution or flow of the recorded film, the effect of the change ofthe recording and production characteristics may be expanded over a widerange by repeated rewriting of these portions.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an informationrecording method capable of greatly increasing the possible number oftimes of repeated rewriting without reducing the recording efficiency ina rewritable high-density information recording method for repeatedlyrewriting information so that the recorded information can be associatedwith both ends of a mark.

It is another object of the invention to provide an informationrecording apparatus capable of greatly increasing the possible number oftimes of repeated rewriting without reducing the recording efficiency ina rewritable high-density information recording method for repeatedlyrewriting information so that the recorded information can be associatedwith both ends of a mark.

The present invention, in order to achieve the first object, providesthe following aspects.

-   1) An information recording method is provided for repeatedly    recording information on a recording medium in association with both    ends of each of marks that are formed to be different in their    physical property from other areas, wherein each time information is    recorded, the marks and the spaces between the marks are    substantially randomly inverted in their positions.

Thereby, when repetitive rewriting is made, the total number of timesthat the marks and spaces are recorded is uniform over all the medium,and therefore the medium is physically uniformly changed by repetitiverecording. Accordingly, the possible number of times of repetitiverewriting can be greatly increased. This does not reduce the informationrecording efficiency at all.

-   (2) The substantially random inversion is made at each record unit.

Here, the record unit is a unit such as a sector that is actuallyrecorded on the recording medium. In other words, any smaller ones thanthese record units are never rewritten as information on the recordingmedium. Of course, it is possible that after the record units arereproduced, only part of the reproduced information is modified andagain recorded as in the read-modify-write process so that the minimumunit to be recorded can be apparently reduced. However, even in thiscase, the above-given record units are actually recorded on andreproduced from the medium. If this inversion occurred within the recordunit, a complicated process would be necessary at the time of signalreproduction.

Thereby, the total number of times that marks are recorded in eachrecord unit is uniform over the record unit. Since the reproductionprocess is generally made for each information record unit, the changeof the medium due to repetitive recording of each record unit isuniform, and thus the possible number of times of repetitive rewritingcan be increased.

-   (3) An information recording method is provided for repeatedly    recording information on a recording medium in association with both    ends of each of marks that are formed to be different in their    physical property from other areas, wherein a synchronizing signal    formed of a plurality of marks is provided at the head of an    information recorded portion, and the number of marks of the    synchronizing signal is changed each time information is rewritten    so that the length of the synchronizing signal can be substantially    randomly changed.

Thereby, since the region in which the synchronizing signal is recordedis used as an adjustment region, the position of the informationrecorded portion is substantially randomly changed. Therefore, whenrepetitive rewriting is made, the total number of times that the marksand spaces are repeatedly recorded is uniform over all the medium ineach record unit. Consequently, the recording medium is uniformlychanged in the physical property by the repetitive recording with theresult that the possible number of times of repetitive rewriting can begreatly increased.

-   (4) An information recording method is provided for repeatedly    recording information on a recording medium by forming recorded    marks that are different in their physical property from other areas    so that the information corresponds to both ends of each of the    marks, wherein a synchronizing signal having a plurality of marks    and spaces is provided at the head of the information recorded    portion, and each time the information is rewritten, the number of    the marks or the spaces of the synchronizing signal is changed so    that the length of the synchronizing signal is substantially    randomly changed, and the marks and the spaces between the marks are    substantially randomly reversed in their positions.

Thereby, when repetitive rewriting is made, the total number of timesthat the marks and spaces are repeatedly recorded is more uniform overthe medium, and hence the possible number of times of repetitiverewriting can be more increased.

-   (5) The length of a guard portion which has dummy data and is    provided at the back end of the information recorded portion is    changed depending upon the length of the synchronizing signal    portion. Therefore, the total length of the record unit ranging from    the head of the synchronizing signal portion to the back end of the    guard or dummy data portion is substantially unchanged.

Thereby, since the total length of the record unit is substantiallyunchanged, the change of the beginning end and last end of informationdoes not affect the information recorded portion at the center of theinformation. Therefore, the possible number of times of repetitiverewriting can be suppressed from being reduced by the effect of thechange of the beginning end and back end of information.

-   (6) Each time the information is rewritten, the information    recording start position is substantially randomly changed.

Thereby, when repetitive rewriting is made, the total number of timesthat the marks and spaces are repeatedly recorded can be made moreuniform over the medium. Therefore, the possible number of times ofrepetitive rewriting can be more increased.

-   (7) An information recording method is featured in that the change    of the information recording start position is smaller than that of    the length of the synchronizing signal.

Thereby, the change of the beginning end and back end of informationdoes not affect the central portion of information, or the informationrecorded portion irrespective of the change of the information recordingstart position. Consequently, the possible number of times of repetitiverewriting can be suppressed from being reduced by the effect of thechange of the beginning end and back end of information. Therefore, thepossible number of times of rewriting can be greatly increased.

The present invention, in order to achieve the second object, providesthe following aspects.

-   (8) An information recording apparatus is provided for recording    information on a recording medium by a structure having at least a    record/reproduce head and a recording pulse generation circuit,    further including at least a random signal generation circuit, a    timing generation circuit, and any one of at least a polarity    inverting circuit for inverting the recording pulse polarity in    accordance with a random signal generated from the random signal    generation circuit, and a synchronizing signal generation circuit    having a function to change the length of the synchronizing signal.

Thus, since at least one of the polarity and timing of the recordingpulse can be changed during recording, the total number of times thatthe marks and spaces are repeatedly recorded when repetitive rewritingis made can be made uniform over the medium. Consequently, the possiblenumber of times of repetitive rewriting on the recording medium can beincreased.

Here, the recording pulse is not any one of the pulses themselves ofheat, light and magnetic field to be applied to the medium at the timerecording on the medium. The actual pulse to be applied to the medium isformed after being converted by a recording pulse shaping circuit or thelike into a multi-pulse train or the like depending on thecharacteristic of the medium, and then recorded.

-   (9) In addition, the recording pulse is passed through a    synthesizing circuit after the generation of the synchronizing    signal, coded data and dummy data, and then its polarity is    inverted.

Thus, the polarity can be surely inverted without dependence on theencoding circuit and system for recording.

(10) The polarity of the synchronizing signal generated from thesynchronizing signal generation circuit is at least changed inaccordance with the above-mentioned random signal.

Thus, since the polarity of the recording pulse can be automaticallyinverted without additionally providing a polarity inverting circuit,the apparatus can be fabricated at low cost.

As described above, according to the present invention, there isprovided an information recording method for recording information onthe medium in a form of an array of recorded marks so that the “0”s or“1”s of binary information are made associated with both ends of each ofthe recorded marks, and featured in that if the same information isrecorded a plurality of times, an array of recorded marks recorded onthe medium according to the information includes an array in which therecorded marks and the spaces between the marks are inverted in theirpositions. Therefore, even though the same information is repeatedlyrecorded on the medium, the marks are not formed at a particularlocation, but can be uniformly formed over the medium by an energy beam,and thus the life of the recording medium can be expanded.

Moreover, the recording medium of the invention has formed along tracksa plurality of sectors each of which has a data region in which therecording data is recorded, a synchronizing signal region providedbefore the data region, and a dummy data region provided after the dataregion, the length of the synchronizing signal region included withineach sector being not constant, the length of the range from the head ofthe synchronizing signal region to the back end of the dummy data regionbeing constant.

Furthermore, a preferred embodiment of the medium has formed alongtracks a plurality of sectors each of which has a data region in whichthe recording data is recorded, first and second regions provided beforeand after the data region, and an identification information portionprovided before the first region, the length of the first region withineach sector being not constant, the length of the range from the head ofthe first region to the back end of the second region being constant,the distance from the head of the first region to the back end of theidentification information portion being not constant.

Thus, the recording medium is deteriorated uniformly by the irradiationof energy beam, and hence high reliability can be ensured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are a conceptional diagram and a pulse waveform diagramfor explaining one embodiment of an information recording method of thepresent invention;

FIG. 2 is a plan view showing another embodiment of the informationrecording method of the present invention;

FIG. 3 is a plan view showing still another embodiment of theinformation recording method of the present invention;

FIG. 4 is a plan view of showing a further embodiment of the informationrecording method of the present invention;

FIG. 5 is a block diagram of an information recording apparatus showingan embodiment of the present invention;

FIG. 6 is a plan view of for explaining one example of the prior artinformation recording method;

FIG. 7 is a graph showing the effect and drawbacks of the prior artinformation recording method;

FIG. 8 is a graph showing the effect of the information recording methodaccording to the present invention; and

FIG. 9 is a circuit block diagram of part of the information recordingapparatus according to the embodiment the present invention inconjunction with FIG. 5.

Other objects, features and advantages of the present invention willbecome apparent from reading of the following description of embodimentsof the invention in conjunction with the accompanying drawings. Likereference numerals and symbols indicate like elements, parts or circuitsin the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will now be described in detail withreference to the drawings.

(Embodiment 1)

FIG. 5 shows an information recording apparatus of an embodiment of theinvention. This apparatus includes a record/reproduce head 32irradiating to a recording medium 8 an energy beam that is based on arecording pulse corresponding to coded recording data of binaryinformation, to form recorded marks on the medium. The “1”s or “0”s ofthe binary information are recorded corresponding to the edges of therecorded marks. This apparatus also includes a pulse conversion circuit34 for reversing the polarity of the recording pulse. Thepolarity-reversed recording pulse may be a pulse of which the leadingedges and trailing edges correspond to either “1”s or “O”s of the binaryinformation.

In this embodiment, a phase-change type optical recording medium(recording film: GeSbTe based material) is used as the recording medium.Therefore, the laser beam is modulated in its intensity, and irradiatedon the recording medium to form recorded marks as amorphous portionswithin a crystal region of the medium.

Referring to FIG. 5, there are shown the record/reproduce head 32 whichrecords and/or reproduces on the recording medium 8, a detection circuit33 which detects the reproduced signal from the record/reproduce head32, and a reproduction circuit 41 which reproduces information from thedetected signal. The reproduction circuit 41 has at least anidentification information detection circuit 42 which detectsidentification information on the medium. The identification informationsignal from the identification information detection circuit 42 issupplied to a timing generation circuit 40, which then generates variousdifferent timing signals for the recording operations.

The apparatus of this embodiment also includes at least a random signalgeneration circuit 36. The random signal generation circuit 36 mayinclude a quasi-random sequence generator or may generate a randomsignal from the information asynchronous with the recording andreproduction operations, such as time or date. The apparatus of thisembodiment further includes an encoding circuit 38 which encodesrecording information (recording data) 50. This encoding circuit 38 isnot necessarily provided within the apparatus depending on the recordingcode.

This embodiment employs (2, 11) RLL coding. A synthesizing circuit 35provided in the apparatus combines the synchronizing signal from asynchronizing signal generation circuit 37, the coded data from theencoding circuit 38, and the dummy data from a dummy data generationcircuit 39 in accordance with a timing signal from the timing signalgeneration circuit 40, to generate coded composite data 51 that is to berecorded as recorded units. The pulse conversion circuit 34 converts thecoded composite data 51 into a recording pulse 53 with the polaritydepending on the random signal 52 produced from the random signalgeneration circuit 36. In this case, the polarity inversion according tothe random signal 52 is made for each record unit. The polarityinversion timing is controlled by a timing signal 54 from the timinggeneration circuit. The recording pulse thus generated is fed to arecording pulse shaping circuit 31 by which it is converted into a pulseform suitable for the record/reproduce head and the recording medium.The shaped pulse is supplied to the record/reproduce head 32 by whichthe energy beam according to this pulse is applied to the recordingmedium 8 to form recorded marks on the medium.

With reference to FIGS. 1A and 1B, a description will be made of therelation between the finally recorded marks and the coded data in thisembodiment.

Referring to FIG. 1A, a coded data sequence “0010000100100001000100” isconverted in NRZI-NRZ scheme into a recording pulse of a form A:“0011111000111110000111 or B: “1100000111000001111000”, by the pulseconversion circuit 34.

The coded data sequence is, for example, a pulse 51 having high levelsat “1”s as shown in FIG. 1B. The pulse conversion circuit converts thispulse 51 into a pulse 53A or a pulse 53B with the polarity opposite tothe pulse 53A.

When the recording pulse 53 is shaped into a multi-pulse train by therecording pulse shaping circuit 31, and then recorded on the medium, amark 6 associated with the “1”s of the recording pulse and a space 7corresponding to the “O”s are formed on the recording medium asillustrated in FIG. 1A. In other words, the mark 6 and the space 7between the marks 6 in the recording pulse A are respectively turnedover in the pulse B to be the space 7 and the mark 6, associated with“0”s and “1”s. Thus, there is no problem in the reproduction even whenthe mark and space are turned over, respectively. This is because thereproduced data from A and B are the same coded data since the signalcorresponding to both ends of the recorded mark 6, or the boundarybetween the mark 6 and the space 7 is detected at the time ofreproduction.

FIG. 9 shows one example of the pulse conversion circuit 34 in thisembodiment. When a timing signal 54 is turned to be at a logical highlevel, the binary random signal 52 is selected as an initial value intoone input of an exclusive logic sum circuit EX-OR to the other input ofwhich the coded composite data 51 is applied. Then, when the timingsignal 54 is turned to be at a logical low level, the exclusive logicsum circuit EX-OR produces the recording pulse signal 53A or 53B, or anexclusive logic sum of the output from the exclusive logic sum circuitEX-OR and the coded composite data including the coded data sequence 51.

In this embodiment, the beginning end of the record mark is randomlyshifted in addition to the inversion of polarity. This random shifttiming control is made by controlling the output timing of thesynthesizing circuit 35 under the timing generation circuit 40. Thetiming generation circuit 40 randomly shifts the recording start timingin accordance with the signal from the random signal generation circuit36.

FIG. 8 shows jitter characteristics obtained when the same data isrepeatedly recorded on one recording medium according to thisembodiment. In FIG. 8, a curve 81 was obtained when the recording startposition was shifted by two bytes, but when there was no polarityinversion. A curve 82 was obtained when the recording start position wassimilarly shifted by two bytes and when polarity inversion was made. Inthis case, the standard deviation of the time shift between thereproduction clock and the reproduced data after the same data wasrecorded repeatedly and then reproduced was normalized by thereproduction detection window width and used as the rate of jitter. FromFIG. 8, it will be obvious that even when the recording start positionis shifted by a small value in the order of two bytes, the possiblenumber of times of rewriting can be increased much more by theadditional polarity inversion in this embodiment than in theconventional apparatus (with no polarity inversion). In this experimentfor the jitter characteristic, the minimum mark length was selected tobe 0.6 μm, and the record/reproduce spot diameter was 0.9 μm.

According to this embodiment, as described above, the marks 6 having thefirst optical property and the spaces 7 having the second opticalproperty are formed on the recording medium, and information associatedwith a binary code of “1”s or “0”s is recorded as an existence ofboundary between a mark and a space. In this recording method, even ifthe same information is recorded a plurality of times, both cases inwhich the boundary corresponding to a particular binary code ofinformation is changed from mark to space and changed from space to markare controlled so as to appear in a plurality of repeated recordingoperations. Thus, the reliability in the recording medium can beincreased.

(Embodiment 2)

Another embodiment of the invention will be described. The informationrecording apparatus of this embodiment is the same as in FIG. 5. Inother words, this apparatus has the record/reproduce head 32 forrecording and/or reproducing on the recording medium 8. The reproducedsignal from the record/reproduce head 32 is detected by the detectioncircuit 33, and the detected signal is fed to the reproduction circuit41 by which information is reproduced from the detected signal. Thereproduction circuit 41 includes at least the identification informationdetection circuit 42 for detecting the identification information on themedium. The identification information signal from the identificationinformation detection circuit 42 controls the timing generation circuit40 to generate various different timing signals for the recordingoperations. The apparatus of this embodiment also has at least therandom signal generation circuit 36. The random signal generationcircuit 36 may include the quasi-random sequence generator, or maygenerate the random signal from the information asynchronous to therecording and reproduction operations, such as time or date.

The apparatus of this embodiment further has the encoding circuit 38which encodes recording information (recording data) 50. This encodingcircuit 38 is not necessarily provided within the apparatus depending onthe recording code.

This embodiment employs (2, 11) RLL coding. The synthesizing circuit 35provided in the apparatus combines the synchronizing signal from thesynchronizing signal generation circuit 37, the coded data from theencoding circuit 38, and the dummy data from the dummy data generationcircuit 39 in accordance with the timing signal from the timing signalgeneration circuit 40, to generate the coded composite data 51 that isto be recorded as recorded units. The synchronizing signal generationcircuit changes the length of the synchronizing signal in accordancewith the random signal generated from the random signal generationcircuit 36. The dummy data generation circuit changes the length of thedummy data in accordance with the random signal generated from therandom signal generation circuit 36. The pulse conversion circuit 34converts the coded composite data 51 into the recording pulse 53 of aparticular polarity. In other words, such polarity inversion as in theprevious embodiment is not made. Thus, the generated pulse is convertedinto a pulse suitable for the actual record/reproduce head and recordingmedium by the recording pulse shaping circuit 31, and therecord/reproduce head 32 applies the energy beam according to the shapedpulse on the recording medium 8 to form the recorded marks on themedium.

In this embodiment, the recording information is recorded to be arrangedon the recording medium as illustrated in FIG. 2. In other words, thesynchronizing signal portion 22 which may be considered as a guardportion is placed at a position separated about a certain distance fromthe identification information 24 that indicates the head of the sector21, and the length of the synchronizing signal portion 22 is changed ateach sector 21. The synchronizing signal portion 22 is followed by theinformation recorded portion 23 and the guard portion 25 in this order.The length of the synchronizing signal portion is changed in accordancewith the random signal generated from the random signal generationcircuit 36. The length of the dummy data is changed by the dummy datageneration circuit 39 in accordance with the random signal generatedfrom the random signal generation circuit 36. At this time, the distancefrom the head of the synchronizing signal to the back end of the guardportion is kept substantially constant.

Thus, even if the data in the information recorded portion is the sameas in the previous recording, the information recorded portion 23 can bemoved back and forth so that the position of the information recordedportion 23 on the medium is randomly changed. As a result, the totalnumber of times of recording marks and spaces is kept uniform over allpositions on the recording medium. Thus, the change of the recordingmedium due to the repeated recording can be averaged so that thepossible number of times of repeated rewriting can be increasedsimilarly to the prior art that is the mark position recording, althoughthis embodiment is the mark-edge recording. In this case, since therecording start position and recording end position are respectivelymaintained to be substantially unchanged unlike the operation of theconventional apparatus. Therefore, even if the amount of shift of theinformation recorded portion 23 is selected to be about 30 to 100 bytes,the change of the recording and reproduction characteristic of themedium at around the recording start point and recording end point doesnot affect the recorded portion. Accordingly, the information recordedportion 23 can be easily shifted by a large amount, thus making itpossible to increase the possible number of times of rewriting.

According to this embodiment, there is provided an information recordingmethod in which a record mark is formed in the data region of therecording medium, and information is recorded in association with bothends of the record mark, as described above. In this method, first andsecond adjustment regions are provided at the front and back ends of thedata region, and changed in their lengths so that the data region isshifted in its position. In addition, when the same information isrecorded a plurality of times, the arrays of a plurality of record marksformed on the recording medium in association with the same informationinclude opposite arrays in which the record marks and the spaces betweenthe record marks are inverted as opposed to the former arrays.

(Embodiment 3)

This embodiment employs the same apparatus as Embodiment 2. The lengthof the synchronizing information is changed. In this case, thesynchronizing information includes a first synchronizing informationportion 221 (VFO) that has marks 6 and spaces 7 of the same lengthalternately and repeatedly arranged in turn, and the length of thesynchronizing information portion 221 and its polarity at the end arechanged. Specifically, the polarity is automatically changed dependingon whether the total number of marks and spaces is even or odd. Inaddition, a second synchronizing information portion 222 (SYNC) isprovided to follow the first synchronizing information portion 221. Thissecond synchronizing information portion 222 has a fixed pattern, butits polarity is changed depending on the polarity of the final end ofthe first synchronizing information portion 221.

FIG. 3 shows examples (A), (B) of the first synchronizing informationportion 221 in which the total number of marks and spaces is odd, and anexample (C) of the first synchronizing information portion 221 in whichthe total number of marks and spaces is even.

Since this embodiment is capable of making polarity inversion withoutany polarity inverting circuit, the recording apparatus is simple inconstruction. In addition, since the information recorded portion 23 canbe shifted in its position, the accumulated number of times that themarks and spaces are recorded is more uniform over the recording medium.Thus, the medium is more uniformly changed by repeated recording withthe result that the possible number of times of repeated rewriting canbe increased more than in Embodiment 1.

(Embodiment 4)

This embodiment employs the same apparatus as Embodiment 3. As shown inFIG. 4, the length of the first synchronizing information portion 221 israndomly changed, and also the recording start position of the firstsynchronizing information portion 221 is changed in accordance with therandom signal. The amount of shift of the recording start position issubstantially equal to the length of the marks (˜¼byte) within the firstsynchronizing information portion 221. Thus, since the total number oftimes at which the marks and spaces within the synchronizing informationportion are recorded is uniform over all the medium, the possible numberof times of repeated rewriting is increased more than in Embodiment 3.In addition, since the amount of shift of the recording start positionis small enough, the recording start position can be considered not tobe changed from the standpoint of the change of recording andreproduction characteristics at around the recording start position.Thus, there is no adverse effect of shift which appears in the priorart.

Since the marks and spaces are repeatedly recorded while they are turnedover at each repetition, the total number of times by which the marksand spaces are repeatedly recorded, or rewritten is uniform over all therecording medium. Thus, the recording medium is uniformly changed byrepetitive recording so that the possible number of times of repeatedrewriting can be greatly increased. This does not reduce the informationrecording efficiency at all. In addition, since the position of theinformation recorded portion on the medium is randomly changed when thelength of the synchronizing signal portion at the head of theinformation recorded portion is randomly changed, the total number oftimes by which the marks and spaces are repeatedly recorded is uniformover all the medium. Therefore, the recording medium is uniformlychanged by repetitive recording, and hence the possible number of timesof repetitive rewriting can be increased.

1. A rewritable recording medium, comprising: a first adjustment regionrecorded with first signal information; a data portion recorded withdata information after the first adjustment region; and a secondadjustment region recorded with second signal information after the dataportion; wherein each time the first signal information is rerecorded, alength of the first adjustment region changes and a start position ofthe first adjustment region changes.